A method for laser welding of titanium / aluminum with coaxial gas flow and pre-placed powder

Abstract

A method for laser welding of titanium / aluminum using coaxial airflow and pre-placed powder-assisted welding comprises the following steps: S1, machining a powder-filling groove on the surface of the aluminum alloy workpiece to be welded; S2, grinding and cleaning the surfaces of the titanium alloy workpiece to be welded and the machined aluminum alloy workpiece; S3, filling the powder-filling groove with pre-prepared metal powder, wherein the pre-prepared metal powder is pure Zr powder, pure V powder, or pure Nb powder; S4, lapping the aluminum alloy workpiece and titanium alloy workpiece to be welded with the titanium alloy workpiece on top and the aluminum alloy workpiece on the bottom to form a lap joint assembly, fixing it on a welding fixture, and covering it with a gas protective cover; S5, welding the assembly using a oscillating laser, during which protective gas is introduced through the gas pipe of the gas protective cover, and a pulsed coaxial protective gas flow is delivered to the welding position in real time through a coaxial gas delivery device. This invention solves the problem of difficulty in controlling the thickness of the brittle intermetallic compound layer during titanium-aluminum dissimilar metal welding.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar material processing, specifically involving a method for laser welding of titanium / aluminum using coaxial airflow and pre-placed powder. Background Technology

[0002] In recent years, lightweight and high-performance structures have received increasing attention and development in order to reduce weight and save energy. Titanium has the advantages of high specific strength, light weight, and good corrosion resistance, but titanium alloys are expensive and are easily oxidized and cracked during welding. Aluminum has the advantages of low weight and low cost. If aluminum alloys are used to replace part of the titanium alloys, the requirements of low cost, lightweight, and high performance can be met. Currently, titanium-aluminum composite structures are widely used in the manufacture of products such as aircraft cabin heat sinks, seat rails, wing honeycomb sandwich panels, and high-speed train carriages. Therefore, using titanium-aluminum composite structures to replace single titanium alloys or aluminum alloys has good development prospects.

[0003] However, due to the significant differences in properties between titanium and aluminum, brittle intermetallic compounds such as TiAl3 and TiAl are easily formed during welding. Because these compounds are hard and brittle, cracks initiate at the brittle intermetallic compound layer when the joint is under load. The cracks propagate along the brittle intermetallic compound layer, eventually causing the joint to fracture. Furthermore, inadequate protection during welding can also lead to cracking in the titanium alloy, reducing joint performance. Therefore, to prevent brittle fracture during service, the type and thickness of the brittle intermetallic compound layer should be controlled, and protective measures should be taken during welding to prevent oxidation and crack formation in the titanium alloy.

[0004] Lasers possess advantages such as high energy density, narrow heat-affected zone, minimal workpiece deformation, and high welding efficiency, leading to their widespread application in dissimilar metal welding. Compared to traditional arc welding of dissimilar metals, laser heat sources are precisely controllable, effectively reducing the peak joint temperature and preventing severe metallurgical reactions. Oscillating lasers can uniformly distribute the heat source, effectively lowering the peak joint temperature and reducing the thickness of the brittle intermetallic compound. However, in actual processing, the dispersion of the heat source after oscillation often leads to instability in the joint metallurgical process, resulting in either excessively thin or excessively thick intermetallic compound layers in certain areas, preventing effective bonding, or stress concentration when the joint is subjected to external stress. Increasing the power can cause severe metallurgical reactions, leading to the formation of thicker brittle intermetallic compounds and reduced joint performance.

[0005] Current research indicates that using alloying elements to regulate the brittle intermetallic compound layer can, to some extent, hinder the interaction between Ti and Al atoms. A third element can react with Ti and Al atoms to form a less brittle phase, or replace Ti or Al atoms in brittle intermetallic compounds such as TiAl3 and TiAl, forming ternary compounds, thereby improving joint performance. Simultaneously, reducing the thickness of the brittle intermetallic compound layer while increasing the joint connection area can effectively improve joint strength. However, most current research focuses on suppressing joint defects such as cracks and porosity by changing the oscillating laser parameters, or on improving joint strength by altering the thickness of the brittle intermetallic compound layer; however, the results are not ideal for titanium-aluminum fusion welding. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of difficulty in controlling the thickness of the brittle intermetallic compound layer during titanium-aluminum dissimilar metal welding. In particular, the current conventional oscillating laser welding cannot solve the problem of uneven metallurgical reaction during dissimilar metal welding. By designing a periodic coaxial airflow and a pre-placed powder-assisted oscillating laser, and adding metal powder welding, a high-performance titanium-aluminum joint is obtained.

[0007] The technical solution adopted by this invention to achieve its objective is: a method for laser welding of titanium / aluminum using coaxial airflow and pre-placed powder, the steps of which are as follows:

[0008] S1. Machining a powder filling groove with a width of 0.5mm-1.5mm and a depth of 0.02mm-0.15mm on the surface of the aluminum alloy workpiece to be welded, parallel to the welding direction along the length direction;

[0009] S2. Grind and clean the surfaces of the titanium alloy workpieces to be welded and the aluminum alloy workpieces after processing.

[0010] S3. Fill the pre-made metal powder into the powder filling trough. The pre-made metal powder is pure Zr powder, pure V powder or pure Nb powder.

[0011] S4. The aluminum alloy workpiece and the titanium alloy workpiece to be welded are overlapped with the titanium alloy workpiece on top and the aluminum alloy workpiece on the bottom to form a lap joint assembly to be welded, and the assembly to be welded is fixed on the welding fixture and covered with a gas protective cover; the filling powder tank is located at the lap joint portion of the lap joint.

[0012] S5. Set the welding path and welding process parameters. Use a oscillating laser to weld the components to be welded. During the welding process, protective gas is introduced through the gas pipe of the gas shield and pulsed coaxial protective gas flow is delivered to the welding position in real time through the coaxial gas delivery device. The coaxial gas delivery device controls the output of coaxial protective gas flow once every 0.08s-0.12s, and the gas flow rate is 50L / min-60L / min. The laser oscillation path of the oscillating laser is circular oscillation, the laser oscillation frequency is 100Hz-150Hz, and the laser oscillation amplitude is 1mm-1.5mm.

[0013] Furthermore, the laser power of the oscillating laser described in this invention is 1900W-2200W, the defocusing amount is +3mm-+5mm, and the welding speed is 25mm / s-35mm / s.

[0014] Furthermore, the coaxial gas delivery device of the present invention includes a high-transparency glass gas chamber connected to the bottom of the laser head of the oscillating laser via a connecting plate. A gas mass flow controller is provided at the position of the gas inlet pipe of the high-transparency glass gas chamber and connected to the gas inlet pipe. An ultra-fine conical gas outlet made of high-transparency glass is provided at the bottom of the high-transparency glass gas chamber for delivering pulsed coaxial protective gas flow to the welding position.

[0015] The laser emitted by the laser passes through a high-transparency glass chamber and an ultra-fine conical air outlet to reach the welding position. Both the high-transparency glass chamber and the ultra-fine conical air outlet are made of high-transparency glass, which will not cause laser loss. The ultra-fine conical air outlet also compresses the airflow, so that the protective airflow acts on the bottom of the keyhole and applies pressure to the bottom of the keyhole.

[0016] Furthermore, the gas protective cover of the present invention includes a protective chamber, a laser scanning groove on the top surface of the protective chamber, and an air inlet on the protective chamber for air to be introduced into the protective chamber. The air inlet is connected to a gas pipe, and protective gas is introduced into the protective chamber through the gas pipe during the welding process.

[0017] Furthermore, the pre-formed metal powder of the present invention has a particle size of 300-500 mesh.

[0018] Furthermore, let L be the length of the overlapping portion of the lap joint of the present invention, and let L be the distance between the filling powder groove and the edge of the aluminum alloy workpiece.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention employs a coaxial gas supply device to deliver pulsed coaxial protective gas flow to the welding area. The protective gas flow acts on the bottom of the keyhole in the molten pool, applying pressure to the bottom of the keyhole, increasing the keyhole size, and increasing the contact area between the liquid aluminum alloy and titanium alloy, allowing for a full reaction between the titanium and aluminum. Subsequently, the gas flow is shut off, the weld depth decreases, the titanium-aluminum reaction weakens, and a thin, brittle metallic compound layer is formed. With the periodic opening and closing of the coaxial protective gas flow, a serrated intermetallic compound layer eventually forms at the joint, increasing the joint bonding area and improving the connection strength. Furthermore, when the joint is subjected to external stress, the serrated intermetallic compound layer can inhibit crack propagation and improve joint strength. Specifically, it includes:

[0021] I. Compared with conventional oscillating laser welding of the same power, the present invention provides more precise control of the molten pool depth. The airflow increases the force on the bottom of the keyhole, which periodically increases the molten depth, causing the interface to form a mechanical interlock, increasing the joint connection area, and increasing the joint connection strength.

[0022] Second, compared with conventional oscillating laser welding of the same power, the welding stability of this invention is significantly enhanced. The addition of pulsed coaxial gas increases the bottom size of the keyhole, making the keyhole less prone to collapse and the molten pool more stable, which can effectively suppress the formation of porosity and spatter.

[0023] Third, compared with conventional oscillating laser welding of the same power, the pulsed coaxial gas of this invention promotes the flow of the molten pool, refines the grains, and solves the problems of heat source dispersion, insufficient diffusion of titanium and aluminum atoms, and uneven metallurgical reaction at the joint caused by oscillation.

[0024] IV. Compared to conventional pre-filled powder welding, this invention allows for the quantitative addition of pre-made metal powder, such as Zr powder, pure V powder, or pure Nb powder, by filling the powder trough to a specific depth. Since Zr, V, or Nb have similar atomic radii to titanium, they can replace titanium atoms in brittle titanium / aluminum intermetallic compounds, causing lattice distortion and enhancing joint strength. Furthermore, Zr, V, or Nb can directly react with titanium and aluminum atoms to form other compounds with lower brittleness, further improving joint performance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a gas protective cover device according to Embodiment 1 of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of the laser welding head according to Embodiment 1 of the present invention.

[0027] Figure 3 This is a force diagram of the bottom of the keyhole in an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of the longitudinal section of the weld in Embodiment 1 of the present invention.

[0029] Figure 5 This is a schematic diagram of the longitudinal section of the weld for comparison. Detailed Implementation

[0030] Example 1

[0031] A 2mm thick TC4 titanium alloy and a 2mm thick 6061-T6 aluminum alloy were joined using a "titanium on top, aluminum on the bottom" method. The welding was performed using the coaxial airflow and pre-placed powder-assisted laser welding method of this invention. The steps are as follows:

[0032] S1. A powder filling groove with a width of 1 mm and a depth of 0.1 mm is machined on the surface of the aluminum alloy workpiece to be welded, parallel to the welding direction along the length direction.

[0033] S2. Grind and clean the surfaces of the titanium alloy workpieces to be welded and the aluminum alloy workpieces after processing.

[0034] S3. Fill the pre-made metal powder into the powder filling trough. The pre-made metal powder is pure Zr powder, pure V powder or pure Nb powder.

[0035] S4. The aluminum alloy workpiece and the titanium alloy workpiece to be welded are overlapped with the titanium alloy workpiece on top and the aluminum alloy workpiece on the bottom to form a lap joint assembly to be welded, and the assembly to be welded is fixed on the welding fixture and covered with a gas protective cover; the filling powder tank is located at the lap joint portion of the lap joint.

[0036] S5. Set the welding path and welding process parameters. Use a oscillating laser to weld the components to be welded. During the welding process, protective gas is introduced through the gas pipe of the gas shield and pulsed coaxial protective gas flow is delivered to the welding position in real time through the coaxial gas delivery device. The coaxial gas delivery device controls the output of coaxial protective gas flow once every 0.12s, and the gas flow rate is 60L / min. The laser oscillation path of the oscillating laser is circular oscillation, the laser oscillation frequency is 100Hz, and the laser oscillation amplitude is 1.3mm.

[0037] The oscillating laser described in this example has a laser power of 2100W, a defocusing amount of +3mm, and a welding speed of 30mm / s.

[0038] The coaxial gas supply device described in this example includes a high-transparency glass gas chamber connected to the bottom of the laser head of the oscillating laser via a connecting plate. A gas mass flow controller is connected to the inlet pipe of the high-transparency glass gas chamber. An ultra-fine conical gas outlet made of high-transparency glass is located at the bottom of the high-transparency glass gas chamber for delivering pulsed coaxial shielding gas flow to the welding position. Before welding, the height of the high-transparency glass gas chamber is adjusted so that the distance from the ultra-fine conical gas outlet to the component to be welded is 10mm.

[0039] Figure 2This is a schematic diagram of the laser welding head in this embodiment. In the diagram, 1 is the collimating lens of the laser head, 2 is the high-speed galvanometer, 3 is the focusing lens, 4 is the protective lens, 5 is the connecting plate, 6 is the connecting bolt, 7 is the high-transparency glass gas chamber, 8 is the gas mass flow controller, 9 is the ultra-fine conical gas outlet, and 10 is the air inlet pipe. In this example, the laser head is connected to a laser, which emits laser light that passes through the collimating lens 1, the high-speed galvanometer 2, the focusing lens 3, the protective lens 4, the high-transparency glass gas chamber 7, and the ultra-fine conical gas outlet 9 to reach the welding position. Both the high-transparency glass gas chamber and the ultra-fine conical gas outlet are made of high-transparency glass, thus preventing laser loss.

[0040] Figure 1 This is a schematic diagram of the gas protective cover device in this embodiment. As shown in the figure, the gas protective cover in this example includes a protective chamber 11, a laser scanning groove 12 on the top surface of the protective chamber 11, and an air inlet 13 on the protective chamber 11 for ventilation. The air inlet 13 is connected to a gas pipe 14, and protective gas is introduced into the protective chamber 11 through the gas pipe 14 during the welding process.

[0041] In this example, the protective gas introduced through the gas pipe of the gas shield during the welding process and the pulsed coaxial protective gas flow delivered to the welding position in real time through the coaxial gas delivery device are both pure argon.

[0042] In this example, the pre-made metal powder has a particle size of 300-500 mesh.

[0043] In this example, the length of the overlapping portion of the lap joint of the present invention is denoted as L, and the distance between the filling powder groove and the edge of the aluminum alloy is 1 / 2 / L.

[0044] Figure 3 This is a force diagram of the keyhole bottom in this embodiment. As can be seen from the diagram, during the oscillating laser welding process, due to energy dispersion, the keyhole opening is large, and the keyhole depth is significantly reduced. After coaxial airflow is introduced into the keyhole through the tapered ultrafine air outlet, the airflow acts on the bottom of the keyhole, causing it to experience downward pressure. The airflow pressure and the reaction force of the liquid metal vapor overcome the surface tension of the liquid metal and gravity, causing the liquid metal at the bottom of the keyhole to flow to the keyhole wall, increasing the keyhole depth.

[0045] Comparative Example

[0046] A 2mm thick TC4 titanium alloy and a 2mm thick 6061-T6 aluminum alloy were joined using a "titanium on top, aluminum on the bottom" lap joint, and conventional single-oscillating laser welding was performed. The steps are as follows:

[0047] S1. Grind and clean the surfaces of the titanium alloy workpiece to be welded and the aluminum alloy workpiece after processing.

[0048] S2. The aluminum alloy workpiece and the titanium alloy workpiece to be welded are overlapped with the titanium alloy workpiece on top and the aluminum alloy workpiece on the bottom to form a lap joint assembly to be welded. The assembly to be welded is fixed on the welding fixture and covered with a gas protective cover.

[0049] S3. Set the welding path and welding process parameters, and use a oscillating laser to weld the components to be welded. During the welding process, protective gas is introduced through the gas pipe of the gas shield. The oscillating laser has a circular oscillation path, a laser oscillation frequency of 100Hz, and a laser oscillation amplitude of 1.3mm. In this example, the laser power of the oscillating laser is 2100W, the defocusing amount is +3mm, and the welding speed is 30mm / s.

[0050] In this example, the gas protective cover includes a protective chamber, a laser scanning groove on the top surface of the protective chamber, and an air inlet on the protective chamber for ventilation. The air inlet is connected to a gas pipe, and during the welding process, protective gas is introduced into the protective chamber through the gas pipe. The protective gas is pure argon.

[0051] A schematic diagram of the welded cross-section effect in Example 1 is shown below. Figure 4 As shown in the diagram, a schematic representation of the welded cross-section effect is as follows: Figure 5 As shown in the figure, welding using the method of this invention enhances the uniformity of the interfacial metallurgical reaction. The titanium alloy and aluminum alloy form a mechanical bond, the intermetallic compound layer at the interface exhibits a serrated connection, the penetration depth is more uniform, and the titanium-aluminum bonding area increases.

Claims

1. A method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder assisted by laser welding, comprising the following steps: S1. Machining a powder filling groove with a width of 0.5 mm-1.5 mm and a depth of 0.02 mm-0.15 mm on the surface of the aluminum alloy workpiece to be welded, parallel to the welding direction along the length direction. S2. Grind and clean the surfaces of the titanium alloy workpieces to be welded and the aluminum alloy workpieces after processing. S3. Fill the pre-made metal powder into the powder filling trough. The pre-made metal powder is pure Zr powder, pure V powder or pure Nb powder. S4. The aluminum alloy workpiece and the titanium alloy workpiece to be welded are overlapped with the titanium alloy workpiece on top and the aluminum alloy workpiece on the bottom to form a lap joint assembly to be welded, and the assembly to be welded is fixed on the welding fixture and covered with a gas protective cover; the filling powder tank is located at the lap joint portion of the lap joint. S5. Set the welding path and welding process parameters. Use a oscillating laser to weld the components to be welded. During the welding process, protective gas is introduced through the gas pipe of the gas shield and pulsed coaxial protective gas flow is delivered to the welding position in real time through the coaxial gas delivery device. The coaxial gas delivery device controls the output of coaxial protective gas flow once every 0.08s-0.12s, and the gas flow rate is 50 L / min-60 L / min. The laser oscillation path of the oscillating laser is circular oscillation, the laser oscillation frequency is 100 Hz-150Hz, and the laser oscillation amplitude is 1 mm-1.5 mm.

2. The method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder as described in claim 1, characterized in that: The oscillating laser has a power of 1900W-2200W, a defocusing amount of +3mm-+5mm, and a welding speed of 25mm / s-35mm / s.

3. The method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder as described in claim 1, characterized in that: The coaxial gas delivery device includes a high-transparency glass gas chamber connected to the bottom of the laser head of the oscillating laser via a connecting plate. A gas mass flow controller is connected to the gas inlet pipe at the position of the high-transparency glass gas chamber's gas inlet pipe. The bottom of the high-transparency glass gas chamber is provided with an ultra-fine conical gas outlet made of high-transparency glass, which is used to deliver pulsed coaxial protective gas flow to the welding position.

4. The method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder as described in claim 1, characterized in that: The gas protective cover includes a protective chamber, a laser scanning groove on the top surface of the protective chamber, and an air inlet on the protective chamber for ventilation. The air inlet is connected to a gas pipe, and protective gas is introduced into the protective chamber through the gas pipe during the welding process.

5. The method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder as described in claim 1, characterized in that: The pre-made metal powder has a particle size of 300-500 mesh.

6. The method for laser welding titanium / aluminum using coaxial airflow and pre-placed powder as described in claim 1, characterized in that: Let L be the length of the overlapping part of the lap joint, and let L be the distance between the powder filling groove and the edge of the aluminum alloy workpiece.

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